#include <stdio.h>
#include <math.h>

float dist(float x1, float y1, float x2, float y2)
{
	return sqrt(pow((x1 - x2), 2) + pow((y1 - y2), 2));
}

int main()
{
	float x1, y1, x2, y2;
	scanf("%f%f%f%f", &x1, &y1, &x2, &y2);
	printf("%.2f", dist(x1, y1, x2, y2));
	return 0;
}